Remove the `Delete Branch` confirmation modal from merged pull requests

[silverwind]

Feature Description

I find this modal annoying and it does not match GitHub behaviour where a merged PR branch is deleted in a single click. I think it's always safe to delete such branches, right?

Screenshots

[delvh]

I think it's always safe to delete such branches, right?

If this branch is fully contained within the main branch, yes.
However, git can't know this when you squash merge or rebase merge.

[delvh]

But yeah, branches that have no commit ahead of them should be deleteable without a modal

[lunny]

Maybe after #6375 resolved.